ANCHORAGE, Alaska  A return to full production at the biggest U.S. oil field after a major spill will take a back seat to Alaska's cleanup and emergency response efforts, state environmental officials said.

A large crude oil spill forced the shutdown of about 100,000 barrels of daily production at the Prudhoe Bay field last Thursday when oil leaked out of a transit pipeline.

Emergency response work takes priority to the full resumption of Prudhoe Bay's daily production, said state officials.

"Everything else is taking precedence," said Lynda Giguere, a spokeswoman for Alaska's Department of Environmental Conservation.

Production at the field averaged about 470,000 barrels in February, according to field operator BP. Other major owners of the field unit are Exxon Mobil Corp. and ConocoPhillips.

BP spokesman Daren Beaudo said the company has been able to divert production of about 5,000 barrels a day and is considering other options since it does not know when production will resume.

Winter conditions have helped mitigate environmental impacts from the oil spill that has spread over nearly two acres of snow-covered tundra and hard-frozen lake, according to the department.

The frigid winter conditions makes it easier to clean up the spilled oil than would have been the case during a time of thaw, said a state official.

"It certainly would have been a lot worse (in the summer). We have probably two months to work on this thing, and it happened at the right time of year," said Ed Meggert, an on-scene response coordinator for the state.

The spilled oil most likely penetrated through the snow layer and reached the tundra surface since the oil pumped out of the wells is hot and typically melts much of the snow, Meggert said.

The leak in the transit line to ship oil out of the Prudhoe Bay field to the trans-Alaska pipeline forced the shutdown of one of the field's six gathering centers.

The affected gathering center separates the oil, natural gas and water pumped out of the wells and processes 100,000 barrels a day from about 230 wells on 12 drill pads, according to BP.

Environmental regulators and BP officials still did not know the exact size of the spill or its environmental impacts.

Cleanup workers who have been at the site have recovered 56,070 gallons of an oil-water mixture, according to a Department of Environmental Conservation report issued Tuesday morning. Officials are expected to calculate the entire spill size by Wednesday, according to the department.

Environmentalists pointed to the spill as evidence that oil development in the Arctic National Wildlife Refuge would threaten the environment there.

"No matter how hard they oil industry tries with new technology and good intentions, mistakes happen," said Eleanor Huffines, director of The Wilderness Society's Alaska office.